Inheriting constructor from parent class in scala

Question

I'm trying to understand the syntax for inheriting one class from another and it seems I must announce the constructor parameters of the parent when I create the child?

Why does this code not compile?

  class Animal(name:String)
  class Dog extends Animal //Here is where compiler error occurs

But this does

  class Animal(name:String)
  class Dog(name:String ) extends Animal(name)

Is their a reason I must explicitly say extends Animal(name) and not just extends Animal and the constructor be implied?

DNA · Accepted Answer · 2016-03-26 17:32:56Z

4

The Scala Language Specification doesn't (as far as I can see) discuss the reasons, but providing an implied constructor would be a special case, and would arguably be less clear.

Note that you can do things like:

class Animal(name:String)
class Dog extends Animal("Dog")

and

class Animal(name:String)
class Dog(n1: String, n2: String) extends Animal(n1 + n2)

So the current behaviour accommodates a variety of patterns in a uniform and explicit way.

answered Mar 26, 2016 at 17:32

DNA

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Comments

Alexey Romanov · Accepted Answer · 2016-03-26 18:07:25Z

1

Let's say you have two constructors for Animal:

class Animal(name:String) {
  def this() = this("unnamed")
}

Which of them would you expect class Dog(name:String) extends Animal to use?

answered Mar 26, 2016 at 18:07

Alexey Romanov

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